AoC 2017 Day 21: Grid Joining

grid-join.go

func join(gs []grid) grid {
	n := int(math.Sqrt(float64(len(gs))))  // Number of subgrids across/down the new grid
	sgn := len(gs[0])                      // Number of values on one side of a subgrid
	cg := newGridBySize(n * sgn)           // The new, combined grid to populate

	// Add each subgrid to the new, combined grid.
	for i, g := range gs {
		// Calculate the position of the top-left of the subgrid once placed in
		// the new, combined grid. We use this plus the offset within the subgrid
		// to place the values in the combined grid.
		tly := (i / n) * sgn
		tlx := (i % n) * sgn

		for j, row := range g {
			for k, cell := range row {
				cg[tly+j][tlx+k] = cell
			}
		}
	}

	return cg
}